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Hi -- I would like to use the NanoVNA for measuring and adjusting antennas in the field for relatively casual POTA and other portable ham radio activities (e.g. tuning the loading coil on a vertical; or tuning wire lengths on a dipole or EFHW; etc).

My antennas' feed points as well as my feed lines are all either UHF or BNC, and my radio has a UHF connector.

The problem is that the NanoVNA has SMA connectors and only an SMA calibration set. In order to measure my antennas and cables I need to use adapters.

Do I need to acquire or make BNC and UHF calibration sets for this kind of field antenna measurement? Or is calibration using the SMA cal set at all useful for this kind of amateur radio activity? I know it's not ideal but since I'm not looking for a high degree of precision I wonder how bad the error will be.

How can I measure the error due to the use of adaptors?


Thanks,

Connie

The only way to properly measure an antenna is at the antenna initially.? Once you're happy with the antenna the coax can mostly be ignored and you should NOT change your antenna based on any measurements done with the coax connected.? Coax has it's own inductance and reactance and impedance which you cannot change.? This is also why tuners are best placed at the antenna and not at the rig as the tuner can get misled by common mode also and coax effects.
If the VNA allows proper calibration you can calibrate your coax by putting the open/short/load at the end of the coax where you are hooking up the antenna.? Then when you measure at the rig side you will see just the antenna (plus whatever common mode is coming back at you) and it should like the measurement done at the antenna.? ?To see if common mode is affecting your measurement you can add a 1/4 lambda length coax jumper and see if your VNA answer changes.? If it does than common mode is affecting your measurement and you can pretty much ignore what the VNA says at that point.
Adapters don't cause a lot of problems so an SMA/PL-259 or SMA/UHF adapter should be OK so at least you are using the same loads all the time (there is (or rather should be) some minor variation between loads).
What you should look for is tuning at the antenna for j0=0 (resonance) -- the frequency where j0=0 occurs should not change with the coax even if common mode occurs.? The rest of the curve might change though.? ? The reason is that you don't get much common mode at the resonant frequency.
I just went through this exercise tuning a 6M beam where we found a Cushcraft 6M4EL had the wrong measurements in the manual.? Once we got the antenna tuned properly (adjusting the feed element for frequency and D1 for impedance) we were able to get an SWR of 1.07 and 600KHz width < 1.5.? Once we connected the coax the tuned frequency stayed the same but the SWR increased a bit to 1.12 which is expected due to the added connectors.? A proper choke at the antenna suppressed common mode on the non-resonant frequencies so the VNA smith chart didn't change much with the coax added.
Mike W9MDB

If you are tuning by SWR only, that won't change due to having the extra stuff between the nanoVNA and the DUT. The values of complex impedance etc will change, though, so if you are using them or Smith charting to do the tuning you can electrically "move" the calibration plane using the method shown in

Here's one way to approach this on an ongoing basis:I did a cal, then put the extension cable onto the nano and worked out its electrical delay and wrote it down. Then did the same for the SMA F-F adapter and for each of my three adapters SMA-BNC/UHF/N. Since I'll usually use the cable, F-F, and one of the adapters I added up the total of those three combinations. That got close, but when I put one of them on it still wasn't quite right, so I played around with the delay setting until I got it as close as I cared to get it back to the original point. In the future I can just recall that cal and apply the electrical delay for that collection of items and know I am seeing reliable results. It's actually really easy once you play with it a bit.

Thus is insteresting

On Thu, Oct 13, 2022 at 12:52 PM Michael Black via groups.io <mdblack98=
[email protected]> wrote:

The only way to properly measure an antenna is at the antenna initially.
Once you're happy with the antenna the coax can mostly be ignored and you
should NOT change your antenna based on any measurements done with the coax
connected. Coax has it's own inductance and reactance and impedance which
you cannot change. This is also why tuners are best placed at the antenna
and not at the rig as the tuner can get misled by common mode also and coax
effects.
If the VNA allows proper calibration you can calibrate your coax by
putting the open/short/load at the end of the coax where you are hooking up
the antenna. Then when you measure at the rig side you will see just the
antenna (plus whatever common mode is coming back at you) and it should
like the measurement done at the antenna. To see if common mode is
affecting your measurement you can add a 1/4 lambda length coax jumper and
see if your VNA answer changes. If it does than common mode is affecting
your measurement and you can pretty much ignore what the VNA says at that
point.
Adapters don't cause a lot of problems so an SMA/PL-259 or SMA/UHF adapter
should be OK so at least you are using the same loads all the time (there
is (or rather should be) some minor variation between loads).
What you should look for is tuning at the antenna for j0=0 (resonance) --
the frequency where j0=0 occurs should not change with the coax even if
common mode occurs. The rest of the curve might change though. The
reason is that you don't get much common mode at the resonant frequency.
I just went through this exercise tuning a 6M beam where we found a
Cushcraft 6M4EL had the wrong measurements in the manual. Once we got the
antenna tuned properly (adjusting the feed element for frequency and D1 for
impedance) we were able to get an SWR of 1.07 and 600KHz width < 1.5. Once
we connected the coax the tuned frequency stayed the same but the SWR
increased a bit to 1.12 which is expected due to the added connectors. A
proper choke at the antenna suppressed common mode on the non-resonant
frequencies so the VNA smith chart didn't change much with the coax added.
Mike W9MDB
On Thursday, October 13, 2022 at 02:10:17 PM CDT, Connie Stillinger
via groups.io <stillinger@...> wrote:

Hi -- I would like to use the NanoVNA for measuring and adjusting
antennas in the field for relatively casual POTA and other portable ham
radio activities (e.g. tuning the loading coil on a vertical; or tuning
wire lengths on a dipole or EFHW; etc).

My antennas' feed points as well as my feed lines are all either UHF or
BNC, and my radio has a UHF connector.

The problem is that the NanoVNA has SMA connectors and only an SMA
calibration set. In order to measure my antennas and cables I need to
use adapters.

Do I need to acquire or make BNC and UHF calibration sets for this kind of
field antenna measurement? Or is calibration using the SMA cal set at
all useful for this kind of amateur radio activity? I know it's not ideal
but since I'm not looking for a high degree of precision I wonder how bad
the error will be.

How can I measure the error due to the use of adaptors?


Thanks,

Connie

On Thu, Oct 13, 2022 at 01:22 PM, <aackthpt@...> wrote:

...if you are using them or Smith charting to do the tuning
you can electrically "move" the calibration plane using the method shown in


...

This video plus your description of how you did it is just what I was looking for.

(also the other replies in this thread are really useful too)

Thanks, folks!

If you just need to tune an antenna "on frequency" you do not even need to calibrate your VNA; it will show the S11 return loss dip at the correct frequency; the magnitude will be wrong but it is not relevant in this case, you are only looking ofr a minimum. I do this when tuning my loop antenna and it works fine. At HF, the error intorduced by adding an adapter after calibration is small.
73, Don N2VGU

The S11 minimum return loss does not indicate resonance.? Common mode current can affect the value and thus the SWR and mislead you when you are not measuring at the antenna.Only J0=0 indicates resonance.??
Mike W9MDB

At HF (1.8 through 30 MHz) the influence of adaptors is pretty minimal.
Above that, yes, you need to cal. with the adaptors and the appropriate
cal. kit(s). This should not be considered a 1 or 0 hard wall, but rather
"fuzzy".

Dave - W?LEV

On Thu, Oct 13, 2022 at 7:10 PM Connie Stillinger via groups.io <stillinger=
[email protected]> wrote:

Hi -- I would like to use the NanoVNA for measuring and adjusting antennas
in the field for relatively casual POTA and other portable ham radio
activities (e.g. tuning the loading coil on a vertical; or tuning wire
lengths on a dipole or EFHW; etc).

My antennas' feed points as well as my feed lines are all either UHF or
BNC, and my radio has a UHF connector.

The problem is that the NanoVNA has SMA connectors and only an SMA
calibration set. In order to measure my antennas and cables I need to
use adapters.

Do I need to acquire or make BNC and UHF calibration sets for this kind of
field antenna measurement? Or is calibration using the SMA cal set at
all useful for this kind of amateur radio activity? I know it's not ideal
but since I'm not looking for a high degree of precision I wonder how bad
the error will be.

How can I measure the error due to the use of adaptors?


Thanks,

Connie

--
*Dave - W?LEV*
*Just Let Darwin Work*


--
Dave - W?LEV

On Fri, Oct 14, 2022 at 09:53 AM, W0LEV wrote:

At HF (1.8 through 30 MHz) the influence of adaptors is pretty minimal.
Above that, yes, you need to cal. with the adaptors and the appropriate
cal. kit(s). This should not be considered a 1 or 0 hard wall, but rather
"fuzzy".

Dave - W?LEV

This is an enormously useful insight for my use case. With this information, along with some of the other tips here, I spent several hours this afternoon with my NanoVNA and my portable adjustable coil vertical HF antenna in the back yard. (Wolf River coils Silver Bullet if anyone is interested.) It makes sense that adapters are pretty small compared to wavelength for HF so for road-trip ham radio use cases their effect can be ignored.

With an adaptor and the knowledge that I could relax about it, I was able to pretty easily and quickly adjust my antenna to be tuned pretty well on 10m, 20m, 40m. In all cases I was able to get ~0j and a low SWR. Good enough to get a bunch of QSOs from California across the country on 20 watts, including my first NJ contact.

My radio does have a built-in SWR meter and antenna tuner but I don't like the way it sweeps the frequencies with a couple of watts, which is basically a transmission. Also SWR is not a great measure of what I really want from my antenna -- which is resonance, namely no reactance at the frequency of interest, as several people pointed out. By adjusting my antenna with the NanoVNA I can get great results for portable ham operation without using the tuner in my radio.

Excellent use of the NANO's. I have gone to including one of the NANOVNA's
in our standard (electronic) camping equipment. They are invaluable in any
portable setup.

Dave - W?LEV

On Sat, Oct 15, 2022 at 3:20 AM Connie Stillinger via groups.io <stillinger=
[email protected]> wrote:

On Fri, Oct 14, 2022 at 09:53 AM, W0LEV wrote:

At HF (1.8 through 30 MHz) the influence of adaptors is pretty minimal.
Above that, yes, you need to cal. with the adaptors and the appropriate
cal. kit(s). This should not be considered a 1 or 0 hard wall, but

rather

"fuzzy".

Dave - W?LEV

This is an enormously useful insight for my use case. With this
information, along with some of the other tips here, I spent several hours
this afternoon with my NanoVNA and my portable adjustable coil vertical HF
antenna in the back yard. (Wolf River coils Silver Bullet if anyone is
interested.) It makes sense that adapters are pretty small compared to
wavelength for HF so for road-trip ham radio use cases their effect can be
ignored.

With an adaptor and the knowledge that I could relax about it, I was able
to pretty easily and quickly adjust my antenna to be tuned pretty well on
10m, 20m, 40m. In all cases I was able to get ~0j and a low SWR.
Good enough to get a bunch of QSOs from California across the country on
20 watts, including my first NJ contact.

My radio does have a built-in SWR meter and antenna tuner but I don't
like the way it sweeps the frequencies with a couple of watts, which is
basically a transmission. Also SWR is not a great measure of what I
really want from my antenna -- which is resonance, namely no reactance at
the frequency of interest, as several people pointed out. By adjusting my
antenna with the NanoVNA I can get great results for portable ham operation
without using the tuner in my radio.

--
*Dave - W?LEV*
*Just Let Darwin Work*


--
Dave - W?LEV